Appraisal of Prognostic Interaction between Sidedness and Mucinous Histology in Colon Cancer: A Population-Based Study Using Inverse Probability Propensity Score Weighting.

Colon cancer with different sidedness (right vs. left) and histology (mucinous vs. non-mucinous) may represent different disease entities. We investigated whether the prognostic values of sidedness and histology differed according to each other. We analyzed 81342 patients with stage II-IV colon cancer from the Surveillance, Epidemiology, and End Results database between 2004 and 2012. Patients were divided into four subgroups on the basis of sidedness and histology: non-mucinous right-sided, non-mucinous left-sided, mucinous right-sided, and mucinous left-sided subgroups. Among each tumor stage, median overall survival (mOS) was compared between these subgroups after inverse probability propensity score weighting to handle confounding factors. In the stage IV subgroup, the prognosis for non-mucinous left-sided tumors (weighted mOS, 24.5 months) was significantly better than that for non-mucinous right-sided tumors (weighted mOS, 16.5 months; <0.001) and that for mucinous left-sided tumors (weighted mOS, 16.5 months; <0.001), whereas the survival was similar between left-sided and right-sided tumors with the mucinous subtype (weighted mOS, 16.5 months for both; =0.570; test for interaction between sidedness and histology, <0.001), and between mucinous and non-mucinous tumors in the right-sided colon (weighted mOS, 16.5 months for both; =0.207). Similar findings were detected in the stage III subgroup ( <0.001). In the stage II subgroup, the survival was comparable among the four sidedness-histology subgroups (=0.159 and =0.466). In stage III/IV colon cancer, the prognostic value of sidedness differed according to histology, and vice versa. By contrast, neither should be considered in risk stratification for stage II colon cancer.